Laser modules have been widely used as devices to emit a laser beam into an optical fiber. A laser module includes a laser source which emits a laser beam, an optical fiber which receives the laser beam, and a heat-dissipating board which have both the laser source and the optical fiber attached thereto. The laser source and the optical fiber are fixed on the heat-dissipating board and positioned so that a laser beam from the laser source efficiently enters the optical fiber.
Generally, in the laser module, the laser source and the optical fiber are not directly attached to the heat-dissipating board. Instead, a laser mount and a fiber mount are first attached to the heat-dissipating board, and then the laser source and the optical fiber are attached to the laser mount and the fiber mount, respectively. For example, Patent Literature 1 discloses an optical fiber having such a configuration.
However, according to such a laser module, heat generated in the laser source causes great stress on solder which joins the laser mount and the heat-dissipating board together. This may result in displacement of the laser source or may cause damage to the solder. Such problems occur mainly because of a difference between (i) thermal expansion coefficient of the laser mount which is made from AlN (aluminum nitride) or CuW (copper tungsten) and (ii) thermal expansion coefficient of the heat-dissipating board which is made from Cu (copper).
In order to avoid such problems, Patent Literature 2 discloses a technique of fixing the heat-dissipating board and the laser mount with soft solder. Patent Literature 2 teaches that the soft solder can absorb stress resulting from a difference between the thermal expansion coefficients of the heat-dissipating board and the laser mount.